bpf: prevent offloaded programs from running on host via tcx/netkit

[kernel-patches-daemon-bpf]

Pull request for series with
subject: bpf: prevent offloaded programs from running on host via tcx/netkit
version: 3
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1085473

[kernel-patches-daemon-bpf]

Upstream branch: b5c111f
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1085473
version: 3

[kernel-patches-review-bot]

commit f286f4b792493a49741f6b2918406a3e4498869c
Author: Jiayuan Chen <jiayuan.chen@linux.dev>

bpf, xdp: move offload check into dev_xdp_install()

bpf_xdp_link_update() calls dev_xdp_install() directly and bypasses
dev_xdp_attach(), so the offload check that lived in dev_xdp_attach()
does not apply. A user can create an XDP link in SKB or native mode
with a regular program and then replace it via BPF_LINK_UPDATE with an
offloaded program, whose bpf_func is bpf_prog_warn_on_exec(), tripping
the WARN on the first packet.

Fixes: 026a4c28e1db3 ("bpf, xdp: Implement LINK_UPDATE for BPF XDP link")

> diff --git a/net/core/dev.c b/net/core/dev.c
> index e59f6025067c..8635de70efe7 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10359,6 +10359,11 @@ static int dev_xdp_install(struct net_device *dev, enum bpf_xdp_mode mode,
>
>  	netdev_ops_assert_locked(dev);
>
> +	if (prog && mode != XDP_MODE_HW && bpf_prog_is_offloaded(prog->aux)) {
> +		NL_SET_ERR_MSG(extack, "Using offloaded program without HW_MODE flag is not supported");
> +		return -EINVAL;
> +	}
> +

While this check addresses offloaded programs (bpf_prog_is_offloaded()),
does it cover device-bound programs? Looking at dev_xdp_attach(), there
are two distinct checks that were in place:

(1) bpf_prog_is_offloaded() check - now moved to dev_xdp_install()
(2) bpf_prog_is_dev_bound() && !bpf_offload_dev_match() check - still in
    dev_xdp_attach()

A program loaded with BPF_F_XDP_DEV_BOUND_ONLY has dev_bound set to true
but offload_requested set to false, meaning bpf_prog_is_offloaded() will
return false. When bpf_xdp_link_update() calls dev_xdp_install() directly,
could such a device-bound program bypass both checks?

If so, this could allow attaching a device-bound program to an SKB-mode
link, potentially causing the generic XDP runner to execute device-specific
kfuncs that cast the generic xdp_md context to driver-specific structures.

Additionally, if the link is in HW mode, the new check evaluates to false
(mode != XDP_MODE_HW) and validation is skipped. Can a program offloaded
to device A be attached via BPF_LINK_UPDATE to an HW link on device B?
If so, the driver might receive XDP_SETUP_PROG_HW and incorrectly cast
the new program's aux->offload->dev_priv to its own internal structure,
resulting in memory corruption.

This concern was raised by sashiko-bot in v2:
https://lore.kernel.org/bpf/20260425104435.ED443C2BCB5@smtp.kernel.org/

>  	if (dev->cfg->hds_config == ETHTOOL_TCP_DATA_SPLIT_ENABLED &&
>  	    prog && !prog->aux->xdp_has_frags) {
>  		NL_SET_ERR_MSG(extack, "unable to install XDP to device using tcp-data-split");
> @@ -10510,10 +10515,6 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
>  			NL_SET_ERR_MSG(extack, "Native and generic XDP can't be active at the same time");
>  			return -EEXIST;
>  		}
> -		if (!offload && bpf_prog_is_offloaded(new_prog->aux)) {
> -			NL_SET_ERR_MSG(extack, "Using offloaded program without HW_MODE flag is not supported");
> -			return -EINVAL;
> -		}
>  		if (bpf_prog_is_dev_bound(new_prog->aux) && !bpf_offload_dev_match(new_prog, dev)) {
>  			NL_SET_ERR_MSG(extack, "Program bound to different device");
>  			return -EINVAL;

---

AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

In-Reply-To-Subject: bpf, xdp: move offload check into dev_xdp_install()
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/24929498218

[kernel-patches-daemon-bpf]

Forwarding comment 4319515564 via email
In-Reply-To: 20260425105942.223757-3-jiayuan.chen@linux.dev
Patch: https://patchwork.kernel.org/project/netdevbpf/patch/20260425105942.223757-3-jiayuan.chen@linux.dev/

[kernel-patches-daemon-bpf]

Upstream branch: b5c111f
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1085473
version: 3

[kernel-patches-daemon-bpf]

Upstream branch: b5c111f
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1085473
version: 3

[kernel-patches-daemon-bpf]

Upstream branch: 0c7ae13
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1085473
version: 3

[kernel-patches-daemon-bpf]

Upstream branch: f3b8c28
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1085473
version: 3

[kernel-patches-daemon-bpf]

Upstream branch: 18fc650
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1085473
version: 3